The field of the invention is tractor trailer running gears and the invention relates more specifically to trailer connecting dollies of the type commonly used to connect a second trailer to a first tractor-drawn trailer. This first tractor drawn trailer is commonly attached to the tractor by a fifth wheel. It is often desirable to attach a second trailer to the first trailer, and this is commonly accomplished by the use of a dolly which carries a fifth wheel, and is attached to the rear of the first trailer by an "I" bolt or pinnel hook and pin. In several states it is now permissible for a third trailer to be attached, and this likewise has, in the past, been connected to the second trailer through a second dolly.
A major difficulty with the use of such dollies results from the plurality of pivot points which exist at each fifth wheel and also at each "I" bolt and pin. The existence of such pivot points increases the hazard of fishtailing or jack knifing. They further essentially preclude the accurate backing of a multiple trailer rig for any significant distance.
A detachable dolly is shown in U.S. Pat. No. 2,590,962, although a less complex dolly is in more common use. The use of unitized shipping containers has given rise to a detachable wheel bogey and dolly, an example of which is shown in U.S. Pat. No. 3,066,953. When the bogey or dolly is moved to its forward position, however, the rear of the trailer is not properly supported. Other patents relating to tractor trailer attachments are U.S. Pat. Nos. 2,195,636; 3,070,386 and 3,933,374.
There is thus a need for a trailer-connecting dolly which provides improved control for the attachment of two or more trailers to a tractor. This need is especially acute for the attachment of three trailers to a tractor.